A power conversion apparatus is disposed, for example, between a battery and a motor. The power conversion apparatus controls power stored in the battery and supplies the power to the motor. Many subunits (e.g., power module, electric reactor) in a power conversion apparatus, namely, a PCU (power control unit) provided in a hybrid vehicle or an electric vehicle produce heat, and the heat may adversely affect the performance of the power conversion apparatus. Thus, a cooling structure is essential. A variety of such cooling techniques have been proposed (e.g., Japanese Patent Application Laid-Open Publication No. 2015-130735).
The power conversion apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 2015-130735 includes a housing that is divided into a first housing portion (i.e., an upper half) and a second housing portion (i.e., a lower half), and the first and second housing portions are assembled to a single unit. The first housing portion houses a first power converter and a first cooler that are integrated into a unit. The second housing portion serves as a second cooler, and a second power converter is mounted inside the second housing portion. In this manner, the cooler is divided into the first cooler and the second cooler, and the first and second coolers are connected to each other via a connecting coolant passage provided outside the housing. The connecting coolant passage includes a first coolant passage and a second coolant passage. The first coolant passage is formed in a first projection portion that projects from an outer surface of the first housing portion. The second coolant passage is formed in a second projection portion that projects from an outer surface of the second housing portion.
However, since the connecting coolant passage is provided outside the housing in this structure, the size of the housing increases. Furthermore, since the second power converter is mounted inside the second housing portion serving as the second cooler, it is difficult to form a cooling fin or fins in/on the second housing portion. It is also difficult to alter the size of the cooler. Thus, use of this structure is limited to certain applications.